Field of the Invention
The present invention relates to a lens apparatus. In particular, the present invention relates to the lens apparatus which controls driving of a focus lens by a vibrating motor, and to an image pickup apparatus which has the lens apparatus.
Description of the Related Art
As for a lens apparatus used in photography, videography and the like, the type which adopts a vibrating motor as an actuator for a focus lens is known. The feature of the vibrating motor is different from the feature of a magnetic motor in the points of being able to obtain large torque even in low-speed rotation, having high holding force during a stop of the motor, being unaffected by magnetism, and the like.
The vibrating motor is constituted by a vibrating body which is formed by a metallic elastic member having a mechanical-electrical energy convertor (piezoelectric device, electrostrictive element) joined or the like, and a contact body which is in contact with the vibrating body. The vibrating body and the contact body are in pressure contact with each other so as to generate frictional force therebetween. When applying a plurality of frequency signals respectively having phase differences to the piezoelectric device, the vibrating body is vibrated, and driving force is generated by relative movement of the vibrating body and the contact body. For this reason, it has been known that, when the vibrating motor is driven, wear is caused at the contact portion between the vibrating body and the contact body, thereby causing performance deterioration. To reduce the suchlike wear accompanied by the driving of the vibrating motor, Japanese Patent Application Laid-Open No. 2009-106043 discloses the technique of reducing the wear by gradually increasing or decreasing the voltage magnitude applied to a surface acoustic wave actuator when accelerating or decelerating the actuator, and thus aiming to prolong the lifetime.
However, although the technique disclosed in Japanese Patent Application Laid-Open No. 2009-106043 is effective when driving the actuator at constant speed, it takes time to reach the desired speed. For this reason, when the driving speed of the actuator frequently changes, speed responsiveness of the actuator significantly deteriorates.
As described above, the vibrating motor is worn out when it is driven. Therefore, when a lot of driving instructions are given in a short time, namely, when the driving instruction is given frequently, the vibrating motor is resultingly driven frequently, whereby the motor is liable to wear.
Incidentally, an instructing device (demand) for instructing driving of a focus lens is connected to a broadcasting interchangeable lens. Thus, it is possible to instruct the driving of the focus lens by an operation of the demand by a photographer (or videographer). Here, the demand, which has a rotation member to be operated by the photographer, is constituted such that the rotation quantity (demand operation quantity) of the rotation member can be detected by a potentiometer or the like. The interchangeable lens gives the driving instruction to the actuator in accordance with the demand operation quantity of the connected demand. In general, the detection of the demand operation quantity is subjected to sampling at a predetermined period, and the instruction value is output to the actuator at the predetermined period.
For this reason, in the case where the actuator is constituted by the vibrating motor, when the driving of the focus lens is instructed by the demand, the driving instruction is frequently given according to the predetermined period as described above, whereby the vibrating motor is liable to wear. To cope with such inconvenience, it only has to prolong the period at which the demand operation quantity is obtained or the period at which the instruction value is output. However, when such a countermeasure is actually implemented, there is a possibility of bringing a feeling of strangeness in the operation because driving responsiveness of the focus lens to the operation of the demand (a change of a photographed image) deteriorates.